U.S. patent application number 16/370549 was filed with the patent office on 2019-10-03 for solar-reflective roofing granules, roofing products including them, and methods for making the granules and roofing products.
The applicant listed for this patent is CertainTeed Corporation. Invention is credited to Simon Mazoyer, Tracy H. Panzarella, Rachel Z. Pytel.
Application Number | 20190300449 16/370549 |
Document ID | / |
Family ID | 68057700 |
Filed Date | 2019-10-03 |
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United States Patent
Application |
20190300449 |
Kind Code |
A1 |
Panzarella; Tracy H. ; et
al. |
October 3, 2019 |
SOLAR-REFLECTIVE ROOFING GRANULES, ROOFING PRODUCTS INCLUDING THEM,
AND METHODS FOR MAKING THE GRANULES AND ROOFING PRODUCTS
Abstract
The present disclosure relates more particularly to roofing
granules, such as solar-reflective roofing granules, and to methods
for making and using them in roofing products. Provided are, for
example, a collection of solar-reflective roofing granules having a
solar reflectivity of at least 70%, (e.g., at least 80 wt % or even
at least 90 wt %) of the solar-reflective roofing granules of the
collection having a major aspect ratio of at least 4 and a minor
aspect ratio of at least 3. Also provided is a roofing product that
includes a substrate; a bituminous material coated on the
substrate, the bituminous material having a top surface; and a
collection of solar-reflective roofing granules as described herein
disposed on the top surface of the bituminous material, thereby
substantially coating the bituminous material in a region
thereof.
Inventors: |
Panzarella; Tracy H.;
(Norwood, MA) ; Pytel; Rachel Z.; (Newton, MA)
; Mazoyer; Simon; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CertainTeed Corporation |
Malvern |
PA |
US |
|
|
Family ID: |
68057700 |
Appl. No.: |
16/370549 |
Filed: |
March 29, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62651100 |
Mar 31, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 35/62802 20130101;
C04B 41/5025 20130101; C04B 2235/9661 20130101; C04B 2235/95
20130101; C04B 2103/54 20130101; C04B 20/1074 20130101; C04B
35/62695 20130101; C04B 20/1066 20130101; C04B 20/1074 20130101;
C04B 2111/80 20130101; C04B 41/65 20130101; E04D 1/20 20130101;
C04B 41/009 20130101; C04B 18/023 20130101; C04B 18/023 20130101;
C04B 41/533 20130101; C04B 18/023 20130101; E04D 7/00 20130101;
C04B 26/26 20130101; C04B 26/26 20130101; C04B 41/4545 20130101;
C04B 2111/00586 20130101; C04B 20/1066 20130101; E04D 2001/005
20130101 |
International
Class: |
C04B 41/45 20060101
C04B041/45; C04B 26/26 20060101 C04B026/26; C04B 41/00 20060101
C04B041/00; C04B 41/50 20060101 C04B041/50; C04B 41/65 20060101
C04B041/65; C04B 35/626 20060101 C04B035/626; C04B 35/628 20060101
C04B035/628; E04D 1/20 20060101 E04D001/20 |
Claims
1. A collection of solar-reflective roofing granules having a solar
reflectivity of at least 70% of the solar-reflective roofing
granules of the collection having a major aspect ratio of at least
4 and a minor aspect ratio of at least 3.
2. The collection of solar-reflective roofing granules according to
claim 1, wherein in at least 70 wt % of the solar-reflective
roofing granules of the collection the ratio of the major axis to
the minor axis is in the range of 1-2.
3. The collection of solar-reflective roofing granules according to
claim 1, wherein at least 90 wt % of the solar-reflective roofing
granules of the collection have a particle size in the range of
1/4'' US mesh to #50 US mesh.
4. The collection of solar-reflective roofing granules according to
claim 1, wherein at least 50 wt % of the solar-reflective roofing
granules have a particle size in the range of 1/4'' US mesh to #30
US mesh.
5. The collection of solar-reflective roofing granules according to
claim 1, wherein at least 10% by weight of the granules of the
collection have a particle size in excess of #20 mesh.
6. The collection of solar-reflective roofing granules according to
claim 1, having a solar reflectivity of at least 75%.
7. The collection of solar-reflective roofing granules according to
claim 1, wherein the solar-reflective roofing granules of the
collection substantially comprise a base particle having a
solar-reflective coating disposed thereon.
8. The collection of solar-reflective roofing granules according to
claim 1, wherein the collection of solar-reflective roofing
granules is white in color; and has (a*.sup.2+b*.sup.2).sup.1/2
less than 6.
9. A roofing product comprising a substrate; a bituminous material
coated on the substrate, the bituminous material having a top
surface; and the collection of solar-reflective roofing granules
according to claim 1 disposed on the top surface of the bituminous
material, thereby substantially coating the bituminous material in
a region thereof.
10. The roofing product according to claim 9, the roofing product
having a major plane, wherein each roofing granule has a major
axis, a minor axis perpendicular to the major axis, and a
thickness, and wherein for at least 90% of the roofing granules
having a major aspect ratio of at least 4 the major axis and the
minor axis are disposed within 20 degrees of parallel to the major
plane of the roofing product.
11. The roofing product according to claim 9, wherein no more than
30% of granules having a major aspect ratio of at least 4 are
disposed with their major axis or minor axis disposed more than 40
degrees from parallel to the major plane of the roofing
product.
12. The roofing product according to claim 9, wherein no more than
10% of the granules having a major aspect ratio of at least 4 are
disposed with their major axis or minor axis disposed more than 70
degrees from parallel to the major plane of the roofing
product.
13. The roofing product according to claim 9, wherein the roofing
product has a bituminous area fraction of no more than 10% in the
region substantially coated by the solar-reflective roofing
granules of the collection.
14. A method for making a roofing product comprising a substrate; a
bituminous material coated on the substrate, the bituminous
material having a top surface; and the collection of
solar-reflective roofing granules according to claim 1 disposed on
the top surface of the bituminous material, thereby substantially
coating the bituminous material in a region thereof, the method
comprising providing a substrate having a bituminous material
disposed thereon, the bituminous material having a top surface, the
top surface of the bituminous material being in a softened state;
and providing the collection of solar-reflective roofing granules
according to claim 1; orienting the solar-reflective roofing
granules of the collection in a substantially single layer on a
substantially upward-facing first, non-adhesive surface having a
major plane such that for at least 90% of the roofing granules the
major axis and the minor axis are disposed within 20 degrees of
parallel to the major plane of the first non-adhesive surface; and
then transferring the solar-reflective roofing granules of the
collection to the top surface of the softened bituminous material
without substantially changing the orientation of the
solar-reflective roofing granules of the collection.
15. The method according to claim 14, wherein the orienting
includes disposing the solar-reflective roofing granules of the
collection on the first, non-adhesive surface, and then vibrating
the first non-adhesive surface under conditions to cause the
solar-reflective roofing granules of the collection to orient in a
substantially single layer on the first, non-adhesive surface such
that for at least 90% of the roofing granules the major axis and
the minor axis are disposed within 20 degrees of parallel to the
major plane of the first non-adhesive surface.
16. The method according to claim 14, wherein the transferring
includes contacting the top surface of the softened bituminous
material in a substantially downward-facing orientation against the
layer of roofing granules on the first non-adhesive surface,
thereby adhering the granules to the top surface of the softened
bituminous material.
17. A method for making a collection of solar-reflective roofing
granules according to claim 1, the method comprising providing a
formable fireable preceramic material; forming the preceramic
material into a collection of preceramic particles having a high
aspect ratio; and firing the collection of preceramic particles to
provide a collection of granular particles having a high aspect
ratio.
18. The method according to claim 17, wherein the forming is
performed by roll compaction.
19. The method according to claim 18, wherein the roll compactor
includes a mold surface formed on one or more rolls thereof, the
mold surface being configured to form high aspect ratio shapes from
the material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority of U.S.
Provisional Patent Application No. 62/651,100, filed Mar. 31,
2018.
BACKGROUND OF THE DISCLOSURE
1. Field of the Disclosure
[0002] The present disclosure relates generally to roofing
products. The present disclosure relates more particularly to
roofing granules, such as solar-reflective roofing granules, and to
methods for making and using them in roofing products.
2. Technical Background
[0003] Sized mineral rocks are commonly used as granules in roofing
applications to provide protective functions to the asphalt
shingles. Roofing granules are generally used in asphalt shingles
or in roofing membranes to protect asphalt from harmful ultraviolet
radiation. Roofing granules typically comprise crushed and screened
mineral materials, which can be coated subsequently with a binder
containing one or more coloring pigments, such as suitable metal
oxides. The granules are employed to provide a protective layer on
asphaltic roofing materials such as shingles, and to add aesthetic
values to a roof.
[0004] Depending on location and climate, shingled roofs can
experience very challenging environmental conditions, which tend to
reduce the effective service life of such roofs. One significant
environmental stress is the elevated temperature to which roofing
shingles are subjected under sunny, summer conditions.
[0005] Mineral-surfaced asphalt shingles, such as those described
in ASTM D0225 or D03462, are generally used in steep-sloped roofs
to enhance the water-shedding function while adding aesthetically
pleasing appearance to the roofs. The asphalt shingles are
generally constructed from asphalt-saturated roofing felts and
surfaced by pigmented color granules, such as those described in
U.S. Pat. No. 4,717,614. Asphalt shingles coated with conventional
roofing granules are known to have low solar heat reflectivity, and
hence will absorb solar heat, especially through the near infrared
range (700 nm-2500 nm) of the solar spectrum. This phenomenon is
increased as the granules covering the surface become dark in
color. For example, while white-colored asphalt shingles can have
solar reflectivity in the range of 25-35%, dark-colored asphalt
shingles can have solar reflectivity of only 5-15%. Furthermore,
except in the white or very light colors, there is typically only a
very small amount of pigment in the color coating of the
conventional granules that reflects solar radiation well. As a
result, it is common to measure temperatures as high as 77.degree.
C. on the surface of black roofing shingles on a sunny day with
21.degree. C. ambient temperature. Absorption of solar heat may
result in elevated temperatures at the shingle's surroundings,
which can contribute to the so-called "urban heat-island effect"
and increase the cooling load to its surroundings. This not only
increases the demand for indoor cooling energy, but also
contributes to smog formation due to higher surface temperatures.
Hence, it is beneficial to have a surface with increased solar
reflectivity, such as greater than 70 percent, to reduce solar heat
gain, thereby reducing the heat flux entering the building envelope
or reducing surface temperatures for lowering smog formation. It is
therefore advantageous to have roofing shingles that have high
solar reflectivity.
[0006] The surface reflectivity of an asphalt shingle or roofing
membrane largely depends on the solar reflectivity of the granules
that are used to cover the bitumen. Typically, roofing granules are
applied such that about 95 to 97 percent of the shingle surface is
effectively covered by the granules.
[0007] The state of California has implemented a building code
requiring the low-sloped roofs to have roof coverings with solar
reflectivity greater than 70%. However, colored roofing granules,
prepared using current coloring technology, are not generally
capable of achieving such a high level of solar reflectivity. Thus,
in order to reduce solar heat absorption, it has been suggested to
apply coatings externally directly onto the shingled surface of
roofs. White pigment-containing latex coatings have been proposed
and evaluated by various manufacturers. However, the polymeric
coating applied has only limited amount of service life and
requires re-coat after certain years of service. Also, the cost of
adding such a coating on roof coverings can be relatively high.
Other manufactures have also proposed the use of exterior-grade
coatings that were colored by IR-reflective pigments for deep-tone
colors and sprayed onto the roof in the field.
[0008] Solar control films that contain either a thin layer of
metal/metal oxides, or dielectric layers applied through vacuum
deposition, have been commercially available for use in
architectural glasses.
[0009] Many materials have been proposed for use in protecting
roofing from solar heat radiation, such as ceramic grog, recycled
porcelain, and white plastic chips. However, the previously
proposed materials have limited use, and cannot satisfy all
requirements for roofing materials. There is a continuing need for
roofing materials, and especially asphalt shingles, that have
improved resistance to thermal stresses. In particular, there is a
need for roofing granules that provide increased solar heat
reflectivity to reduce the solar absorption of the shingle. Hence,
it would be advantageous to have a granular roofing product that
has solar reflectivity greater than 70%.
SUMMARY OF THE DISCLOSURE
[0010] In one aspect, the present disclosure provides a collection
of solar-reflective roofing granules having a solar reflectivity of
at least 70%, (e.g., at least 80 wt % or even at least 90 wt %) of
the solar-reflective roofing granules of the collection having a
major aspect ratio of at least 4 and a minor aspect ratio of at
least 3.
[0011] In another aspect, the present disclosure provides a roofing
product comprising [0012] a substrate; [0013] a bituminous material
coated on the substrate, the bituminous material having a top
surface; and [0014] a collection of solar-reflective roofing
granules as described herein disposed on the top surface of the
bituminous material, thereby substantially coating the bituminous
material in a region thereof. In certain such embodiments, each
roofing granule has a major axis, a minor axis perpendicular to the
major axis, and a thickness, and for at least 90% of the roofing
granules having a major aspect ratio of at least 4 the major axis
and the minor axis are disposed within 20 degrees of parallel to
the major plane of the roofing product.
[0015] In another aspect, the present disclosure provides a method
for making a roofing product as described herein, comprising [0016]
providing a substrate having a bituminous material disposed
thereon, the bituminous material having a top surface, the top
surface of the bituminous material being in a softened state; and
[0017] providing a collection of solar-reflective roofing granules
as described herein; [0018] orienting the solar-reflective roofing
granules of the collection in a substantially single layer on a
substantially upward-facing first, non-adhesive surface having a
major plane such that for at least 90% of the roofing granules
having a major aspect ratio of at least 4 the major axis and the
minor axis are disposed within 20 degrees of parallel to the major
plane of the first non-adhesive surface; and then [0019]
transferring the solar-reflective roofing granules of the
collection to the top surface of the softened bituminous material
without substantially changing the orientation of the
solar-reflective roofing granules of the collection.
[0020] Another aspect of the disclosure provides a method for
making a collection of solar-reflective roofing granules as
described herein, the method comprising [0021] providing a formable
fireable preceramic material; [0022] forming the preceramic
material into a collection of preceramic particles having a high
aspect ratio (e.g., by roll compaction); and [0023] firing the
collection of preceramic particles to provide a collection of
granular particles having a high aspect ratio. The particles
themselves can in some embodiments be the roofing granules of the
collection, or in other embodiments can be coated to provide the
roofing granules of the collection.
[0024] Additional aspects of the disclosure will be evident from
the disclosure herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The accompanying drawings are included to provide a further
understanding of the methods and devices of the disclosure, and are
incorporated in and constitute a part of this specification. The
drawings are not necessarily to scale, and sizes of various
elements may be distorted for clarity. The drawings illustrate one
or more embodiment(s) of the disclosure, and together with the
description serve to explain the principles and operation of the
disclosure.
[0026] FIG. 1 is a schematic view of a roofing granule suitable for
use in the collections of roofing granules of the disclosure.
[0027] FIG. 2 is a cross-sectional schematic view of a coated
solar-reflective roofing granule of the disclosure.
[0028] FIG. 3 is a cross-sectional schematic view of another
solar-reflective roofing granule of the disclosure.
[0029] FIG. 4 is a schematic cross-sectional view of a roofing
product according to one embodiment of the disclosure.
[0030] FIG. 5 is a schematic view of a method for making a roofing
product according to one embodiment of the disclosure.
[0031] FIG. 6 is a schematic view of another method for making a
roofing product according to one embodiment of the disclosure.
[0032] FIG. 7 is a schematic view of a method for using roll
compaction to form granular particles.
[0033] FIG. 8 is a set of photographs showing staining of example
shinglets.
[0034] FIG. 9 is a set of grayscale intensity maps, and FIG. 10 is
a set of boundary skins for two example shingles using different
size granules.
[0035] FIG. 11 is a graph of solar reflectivity and shingle
roughness for a variety of shingles.
[0036] FIG. 12 is a full view and FIG. 13 is a detail view of a
particle sorter;
[0037] FIG. 14 is graph showing the bin distribution of sorted
granules using the particle sorter of FIG. 12 in a sorting
experiment.
[0038] FIG. 15 is a set of pictures from two bins in the sorting
experiment of FIG. 14.
[0039] FIG. 16 is graph showing solar reflectivities of granules
from various bins from the sorting experiment of FIG. 14.
[0040] FIG. 17 is graph showing solar reflectivities of samples
made from granules from various bins from the sorting experiment of
FIG. 14.
[0041] FIG. 18 is a schematic view of a method to orient granules
and to apply them to a bituminous material according to the
disclosure.
[0042] FIG. 19 is a graph showing solar reflectivities for samples
made from random and flattened oriented granules.
DETAILED DESCRIPTION
[0043] The present inventors have noted that, while
solar-reflective coatings and materials used in roofing granules
can provide a relatively good solar reflectivity to a roofing
product bearing them, additional improvements are necessary. The
present inventors have determined certain aspects of shape, size
and orientation that can provide additional advantages. For
example, the present inventors have noted that the use of
relatively flat solar-reflective roofing granules can provide
additional solar reflectivity to the overall roofing product,
especially when they are oriented such that they are substantially
in the plane of the roofing product. In that regard, the present
inventors have developed new ways for providing the desired
orientation of relatively flat granules on a roofing product.
[0044] The present inventors have also noted that the size of the
roofing granules can be important, with granules in certain size
ranges providing improved reflectivity to the overall roofing
product.
[0045] The present inventors have also determined new methods for
making relatively flat solar-reflective roofing granules, using
methods such as roll compaction to provide the desired shape to the
granules.
[0046] Accordingly, one aspect of the disclosure is a collection of
solar-reflective roofing granules having a solar reflectivity of at
least 70%. At least 70 wt % (e.g., at least 80 wt % or even at
least 90 wt %) of the solar-reflective roofing granules of the
collection have a major aspect ratio of at least 4 and a minor
aspect ratio of at least 3.
[0047] A schematic view of a roofing granule is shown in FIG. 1.
Roofing granule 100 has a major axis 102, extending along the
average plane of the roofing granule along its longest dimension.
In the case of the particular roofing granule shown in FIG. 1, the
longest dimension is along a side of the roofing granule; in other
granules, the longest dimension may be along a diagonal. Roofing
granule 100 also has minor axis 104, extending along the average
plane of the roofing granule and perpendicular to the major axis
102. The minor axis extends along the longest dimension of the
granule in the direction perpendicular to the major axis. Roofing
granule 100 also has a thickness 106, in a direction perpendicular
to the plane of major axis 102 and minor axis 104, taken as the
maximum thickness in that direction. The major aspect ratio is
defined as the ratio of the major axis to the thickness, while the
minor aspect ratio is defined as the ratio of the minor axis to the
thickness.
[0048] In certain embodiments as otherwise described herein, at
least 70 wt % (e.g., at least 80 wt % or even at least 90 wt %) of
the solar-reflective roofing granules of the collection have a
major aspect ratio of at least 6. For example, in certain
embodiments, at least 70 wt % (e.g., at least 80 wt % or even at
least 90 wt %) of the solar-reflective roofing granules of the
collection have a major aspect ratio of at least 8.
[0049] In certain embodiments as otherwise described herein, at
least 70 wt % (e.g., at least 80 wt % or even at least 90 wt %) of
the solar-reflective roofing granules of the collection have a
minor aspect ratio of at least 5. For example, in certain
embodiments, at least 70 wt % (e.g., at least 80 wt % or even at
least 90 wt %) of the solar-reflective roofing granules of the
collection have a major aspect ratio of at least 7.
[0050] The present inventors have noted that a flake-like geometry,
especially in combination with certain granule size ranges, can
provide for increased solar reflectivity and resistance to
staining. Accordingly, in certain embodiments as otherwise
described herein, in at least 70 wt % (e.g., at least 80 wt % or
even at least 90 wt %) of the solar-reflective roofing granules of
the collection the ratio of the major axis to the minor axis is in
the range of 1-2. In certain such embodiments, in at least 70 wt %
(e.g., at least 80 wt % or even at least 90 wt %) of the
solar-reflective roofing granules of the collection the ratio of
the major axis to the minor axis is in the range of 1-1.5, or
1-1.33.
[0051] The person of ordinary skill in the art will appreciate that
the solar-reflective roofing granules can be provided in a wide
variety of sizes. For example, in certain embodiments as otherwise
described herein, at least 90 wt % of the solar-reflective roofing
granules of the collection have a particle size in the range of
1/4'' US mesh to #50 US mesh, e.g., #5 US mesh to #50 US mesh.
[0052] But the present inventors have determined that relatively
larger granules can provide improvements not only in initial solar
reflectivity, but also in resistance to degradation of solar
reflectivity with time. Accordingly, in certain embodiments as
otherwise described herein, least 50 wt % of the solar-reflective
roofing granules have a particle size in the range of 1/4'' US mesh
to #30 US mesh, for example, 1/4'' US mesh to #25 US mesh, #5 US
mesh to 30 US mesh, or #5 US mesh to #25 US mesh. In certain
embodiments, at least 70 wt % (e.g., at least 80 wt % or at least
90 wt %) of the solar-reflective roofing granules (have a particle
size in the range of 1/4'' US mesh to #30 US mesh, for example,
1/4'' US mesh to #25 US mesh, #5 US mesh to 30 US mesh, or #5 US
mesh to #25 US mesh. In certain embodiments, at least 50 wt % of
the solar-reflective roofing granules have a particle size in the
range of 1/4'' US mesh to #20 US mesh, for example, #5 US mesh to
20 US mesh, 1/4'' US mesh to 15 US mesh, #5 US mesh to #15 US mesh,
or #12 US mesh to #20 US mesh, or #16 US mesh or #20 US mesh. For
example, in certain embodiments, at least 70 wt % (e.g., at least
80 wt % or at least 90 wt %) of the solar-reflective roofing
granules have a particle size in the range of 1/4'' US mesh to #20
US mesh, for example, #5 US mesh to 20 US mesh, 1/4'' US mesh to 15
US mesh, #5 US mesh to #15 US mesh, or #12 US mesh to #20 US mesh,
or #16 US mesh or #20 US mesh.
[0053] However, it can be desirable to include some smaller
particles in the granules that are applied to a roofing substrate,
to help fill gaps between larger particles. For example, in certain
embodiments, at least 10% by weight (e.g., at least 15 wt %, at
least 20 wt % or even at least 30 wt %) of the granules of a
collection of roofing granules as otherwise described herein have a
particle size in excess of #20 mesh. And in certain such
embodiments, at least 10% by weight (e.g., at least 15 wt %, at
least 20 wt % or even at least 30 wt %) of the granules of the
collection have a particle size in excess of #30 mesh. Such
gap-filling granules need not have a high aspect ratio as described
herein. Collections of granules that include both high-aspect ratio
granules and lower aspect ratio granules can be the natural result
of a particular granule manufacturing process, or instead can be
made by combining a collection of high-aspect ratio granules as
otherwise described herein with small low-aspect ratio granules,
e.g., either before application to a roofing product or by
application of two different types of granules to a roofing product
in two process operations).
[0054] As used herein, the term "granule" does not apply to
particles having a major dimension smaller than 0.2 mm.
[0055] The mineral roofing granules as described herein can
advantageously have very high solar reflectivity values. As
described above, the collection of solar-reflective roofing
granules of the collection has a solar reflectivity of at least
70%. In certain such embodiments, a collection of mineral roofing
granules as otherwise described herein has a solar reflectivity of
at least 75%, at least 80%, or even at least 85%. Solar
reflectivity of granules is measured of the granules as disposed on
a flat surface (e.g., in a petri dish) packed in a thickness
sufficient such that only granules are visible from above, using a
solar reflectometer pursuant to ASTM C1549.
[0056] The solar-reflective roofing granules can have a variety of
structures. For example, in certain embodiments as otherwise
described herein, the solar-reflective roofing granules of the
collection substantially comprise a base particle having a
solar-reflective coating disposed thereon. By "substantially
comprise" it is meant that nearly all of the solar-roofing granules
of the collection have this structure, but that there may be a
small proportion (e.g., less than 1%) that do not (e.g., by being
incompletely coated).
[0057] Examples of the suitable base particles include crushed
slate, slate granules, shale granules, granule chips, mica granules
and metal flakes with a flake-like geometry.
[0058] In other embodiments, the base particle is a synthetic
particle. As described in more detail below, the present inventors
have determined that base particles having a desired geometry can
be made by a variety of methods from, for example, clays and other
preceramic materials.
[0059] Preferably, the solar-reflective coating applied to the base
particles does not significantly affect the geometry of the
resulting roofing granules. Thus, the coated roofing granules can
have essentially the same geometry as the flat base particles from
which they are formed (e.g., with respect to the aspect ratios and
sizes as described above). The solar reflective coating can,
however, smooth out the surface of the granule to reduce light
trapping by reflection in defects.
[0060] In certain embodiments, the solar-reflective coating is
white in color.
[0061] In certain desirable embodiments, in at least 90 wt % of the
solar-reflective roofing granules of the collection, the surface
area of the base particles is at least 80 percent covered with the
solar-reflective coating, e.g., at least 85 percent, at least 90
percent or even at least 95 percent covered with the
solar-reflective coating, and still more preferably the at least 98
percent covered with the solar-reflective coating. Still more
preferably, in at least 90 wt % of the solar-reflective roofing
granules of the collection, the base particles are encapsulated
completely with the solar heat reflective coating; that is, the
entire surface area of the base particles is covered with the solar
heat reflective coating.
[0062] The composition and the thickness of the solar-reflective
coating can selected to provide solar heat reflective roofing
granules with a solar reflectivity of at least 70%, or any other
desired value. For example, in certain embodiments, the thickness
of the solar-reflective coating is at least one mil (0.001 inch,
2.54.times.10.sup.-5 m), more preferably at least 2 mils, and still
more preferably at least 3 mils. The desired thickness of the
solar-reflective coating will depend upon the concentration of
solar-reflective pigment(s) in the coating and the nature of the
solar-reflective pigment(s) in the coating. Preferably, the coating
is uniform, such that the thickness of the coating does not vary by
more than about 25 percent, more preferably by no more than about
10 percent, from the average coating thickness, at the 95 percent
confidence interval. But different coatings can be formed in
different thicknesses to provide a desired degree of
reflectivity.
[0063] As the person of ordinary skill will appreciate, a variety
of materials can be used as solar-reflective pigments in the
coatings described herein. Examples of clays that can be used
include kaolin, other aluminosilicate clays, Dover clay, bentonite
clay, etc. Titanium dioxides such as rutile titanium dioxide and
anatase titanium dioxide, metal pigments, titanates, and mirrorized
silica pigments can also be used. Other solar-reflective pigments
that can be adapted for use include calcium carbonate, zinc oxide,
lithopone, zinc sulfide, white lead, and organic and inorganic
opacifiers such as glass spheres.
[0064] Examples of mirrorized silica pigments that can be used in
the solar-reflective roofing granules described herein include
pigments such as Chrom Brite.TM. CB4500, available from Bead Brite,
400 Oser Ave, Suite 600, Hauppauge, N.Y. 11788.
[0065] An example of a rutile titanium dioxide that can be employed
in the solar-reflective roofing granules described herein includes
R-101, available from Du Pont de Nemours, P.O. Box 8070,
Wilmington, Del. 19880.
[0066] Examples of metal pigments that can be employed in the
solar-reflective roofing granules described herein include aluminum
flake pigment, copper flake pigments, copper alloy flake pigments,
and the like. Metal pigments are available, for example, from
ECKART America Corporation, Painesville, Ohio 44077. Suitable
aluminum flake pigments include water-dispersible lamellar aluminum
powders such as Eckart RO-100, RO-200, RO-300, RO-400, RO-500 and
RO-600, non-leafing silica coated aluminum flake powders such as
Eckart STANDART PCR 212, PCR 214, PCR 501, PCR 801, and PCR 901,
and STANDART Resist 211, STANDART Resist 212, STANDART Resist 214,
STANDART Resist 501 and STANDART Resist 80; silica-coated
oxidation-resistant gold bronze pigments based on copper or
copper-zinc alloys such as Eckart DOROLAN 08/0 Pale Gold, DOROLAN
08/0 Rich Gold and DOROLAN 10/0 Copper.
[0067] Examples of titanates that can be employed in the
solar-reflective roofing granules described herein include titanate
pigments such as colored rutile, priderite, and pseudobrookite
structured pigments, including titanate pigments comprising a solid
solution of a dopant phase in a rutile lattice such as nickel
titanium yellow, chromium titanium buff, and manganese titanium
brown pigments, priderite pigments such as barium nickel titanium
pigment; and pseudobrookite pigments such as iron titanium brown,
and iron aluminum brown. The preparation and properties of titanate
pigments are discussed in Hugh M. Smith, High Performance Pigments,
Wiley-VCH, pp. 53-74 (2002).
[0068] Examples of near IR-reflective pigments available from the
Shepherd Color Company, Cincinnati, Ohio, include Arctic Black
10C909 (chromium green-black), Black 411 (chromium iron oxide),
Brown 12 (zinc iron chromite), Brown 8 (iron titanium brown
spinel), and Yellow 193 (chrome antimony titanium).
[0069] Aluminum oxide, preferably in powdered form, can be used as
a solar-reflective additive in a color coating formulation to
improve the solar reflectivity of colored roofing granules without
affecting the color. The aluminum oxide should have particle size
less than #40 mesh (425 micrometers), preferably between 0.1
micrometers and 5 micrometers. More preferably, the particle size
is between 0.3 micrometers and 2 micrometers. The alumina should
have a percentage of aluminum oxide greater than 90 percent, more
preferably greater than 95 percent. Preferably the alumina is
incorporated into the granule so that it is concentrated near
and/or at the outer surface of the granule.
[0070] A colored, infrared-reflective pigment can also be employed
in preparing the solar-reflective roofing granules described
herein. Preferably, the colored, infrared-reflective pigment
comprises a solid solution including iron oxide, such as disclosed
in U.S. Pat. No. 6,174,360, incorporated herein by reference. The
colored infrared-reflective pigment can also comprise a near
infrared-reflecting composite pigment such as disclosed in U.S.
Pat. No. 6,521,038, incorporated herein by reference. Composite
pigments are composed of a near-infrared non-absorbing colorant of
a chromatic or black color and a white pigment coated with the
near-infrared non-absorbing colorant. Near-infrared non-absorbing
colorants that can be used include organic pigments such as organic
pigments including azo, anthraquinone, phthalocyanine,
perinone/perylene, indigo/thioindigo, dioxazine, quinacridone,
isoindolinone, isoindoline, diketopyrrolopyrrole, azomethine, and
azomethine-azo functional groups. Preferred black organic pigments
include organic pigments having azo, azomethine, and perylene
functional groups. When organic colorants are employed, a low
temperature cure process is preferred to avoid thermal degradation
of the organic colorants.
[0071] While in some embodiments the coatings are colored, in order
to achieve high solar reflectivity, in one presently preferred
embodiment, the binder, pigment, and ratio of pigment to binder are
selected such that the solar-reflective granules are white in
color. In certain embodiments, the collection of solar-reflective
granules has (a*.sup.2+b*.sup.2).sup.1/2 less than 10, e.g., less
than 6, or even less than 2.5. In certain embodiments the
collection of solar-reflective granules have an L* of at least 75,
more preferably at least 80, still more preferably at least 85, and
even more preferably at least 90. L*, a* and b* can be determined
in the configuration described above with respect to solar
reflectivity of granules.
[0072] Coating materials useful in the granules described herein
can include a coating binder and one or more pigments, for example,
together with functional fillers and/or functional additives for
improved processing, to improve dispersion of pigments, to space
out pigments for optimal scattering, to enhance fire resistance, to
provide algae resistance, etc.
[0073] Preferably, the coating material, including the coating
binder, the pigments employed, and the additives, applied to the
base particles is suitable for roofing applications. Coating
materials which provide coatings with very good outdoor durability
are preferred. It is also preferred that the coating material
employed provide a coating with excellent fire resistance.
[0074] Examples of coating binders that can be used in the granules
described herein include metal silicates, fluoropolymers, metal
phosphates, silica coatings, sol-gel coatings, polysiloxanes,
silicone coating, polyurethane coating, polyacrylates, or their
combinations.
[0075] Coating compositions employed in the granules described
herein can include inorganic binders such as ceramic binders, and
binders formed from silicates, silica, zirconates, titanates,
phosphate compounds, et al. For example, the coating composition
can include sodium silicate and/or kaolin clay.
[0076] Organic binders can also be employed in the granules
described herein. The use of suitable organic binders, when cured
can also provide superior granule surface with enhanced granule
adhesion to the asphalt substrate and with better staining
resistance to asphaltic materials. Roofing granules including
inorganic binders often require additional surface treatments to
impart certain water repellency for granule adhesion and staining
resistance. U.S. Pat. No. 5,240,760 discloses examples of
polysiloxane-treated roofing granules that provide enhanced water
repellency and staining resistance. With the organic binders, the
additional surface treatments may be eliminated. Also, certain
organic binders, particularly those water-based systems, can be
cured by drying at much lower temperatures as compared to the
inorganic binders such as metal-silicates, which often require
curing at temperatures greater than about 500 degrees C. or by
using a separate process to render the coating durable.
[0077] Examples of organic binders that can be employed in the
granules described herein include acrylic polymers, alkyds and
polyesters, amino resins, melamine resins, epoxy resins, phenolics,
polyamides, polyurethanes, silicone resins, vinyl resins, polyols,
cycloaliphatic epoxides, polysulfides, phenoxy, fluoropolymer
resins. Examples of uv-curable organic binders that can be employed
in the granules described herein include uv-curable acrylates,
uv-curable polyurethanes, uv-curable cycloaliphatic epoxides, and
blends of these polymers. In addition, electron beam-curable
polyurethanes, acrylates and other polymers can also be used as
binders. High solids, film-forming, synthetic polymer latex binders
are useful in the granules described herein. Presently preferred
polymeric materials useful as binders include uv-resistant
polymeric materials, such as poly(meth)acrylate materials,
including poly methyl methacrylate, copolymers of methyl
methacrylate and alkyl acrylates such as ethyl acrylate and butyl
acrylate, and copolymers of acrylate and methacrylate monomers with
other monomers, such as styrene. Preferably, the monomer
composition of the copolymer is selected to provide a hard, durable
coating. If desired, the monomer mixture can include functional
monomers to provide desirable properties, such as crosslinkability
to the copolymers. The organic material can be dispersed or
dissolved in a suitable solvent, such as coatings solvents well
known in the coatings arts, and the resulting solution used to coat
the granules. Alternatively, water-borne emulsified organic
materials, such as acrylate emulsion polymers, can be employed to
coat the granules, and the water subsequently removed to allow the
emulsified organic materials of the coating composition to
coalesce. When a fluidized bed coating device is used to coat the
inorganic particles, the coating composition can be a 100 percent
solids, hot-melt composition including a synthetic organic polymer
that is heated to melt the composition before spray
application.
[0078] The coating material can further include one or more
functional additives. Examples of such functional additives include
curing agents for the binder, pigment spacers, such as purified
kaolin clays, and viscosity modifiers. The coating material can
also contain biocides or algaecides for obtaining resistance to
microbial discoloration.
[0079] The solar-reflective coating can be applied to the base
particles by any coating process known in the art. However, coating
processes which provide a uniform coating on the base particles are
preferred. Preferably, the coating weight per unit surface area
varies by no more than ten percent, more preferably by no more than
five percent, and still more preferably, by no more than two
percent. Preferably, the coating completely covers the base
particles. Further, it is preferred that there be no areas of the
base particles which are covered with only a nominal thickness of
coating or which are not coated at all.
[0080] Examples of coating process which can be employed in
preparing the roofing granules described herein include fluidized
bed coating, encapsulation by gelation, chelation, solvent
evaporation, coacervation, vesicle formation, and spinning disk
encapsulation. In certain embodiments of the methods of the
disclosure, fluidized bed coating is preferred. Suitable coating
methods are disclosed in commonly assigned U.S. Patent Application
Publication 2006/0251807 A1, incorporated herein by reference. This
type of coating device is preferably employed to provide a precise
and uniform coating on the surface of the particles. Multiple
coating layers can be applied in a single batch by applying a
sequence of coating materials to the particles through a suitable
spray nozzle. Wurster-type fluidized bed spray devices are
available from a number of vendors, including Glatt Air Techniques,
Inc., Ramsey, N.J. 07446; Chungjin Tech. Co. Ltd., South Korea;
Fluid Air Inc., Aurora, Ill. 60504, and Niro Inc., Columbia, Md.
21045. The nature, extent, and thickness of the coating provided in
a Wurster-type fluidized bed spray device depends upon a number of
parameters including the residence time of the particles in the
device, the particle shape, the particle size distribution, the
temperature of the suspending airflow, the temperature of the
fluidized bed of particles, the pressure of the suspending airflow,
the pressure of the atomizing gas, the composition of the coating
material, the size of the droplets of coating material, the size of
the droplets of coating material relative to the size of the
particles to be coated, the spreadability of the droplets of
coating material on the surface of the particles to be coated, the
loading of the device with the mineral particles or batch size, the
viscosity of the coating material, the physical dimensions of the
device, and the spray rate. Modified Wurster-type devices and
processes, such as, the Wurster-type coating device disclosed in
U.S. Patent Publication 2005/0069707, incorporated herein by
reference, for improving the coating of asymmetric particles, can
also be employed. In addition, lining the interior surface of the
coating device with abrasion-resistant materials can be employed to
extend the service life of the coater.
[0081] Other types of batch process particle fluidized bed spray
coating techniques and devices can be used. For example, the
particles can be suspended in a fluidized bed, and the coating
material can be applied tangentially to the flow of the fluidized
bed, as by use of a rotary device to impart motion to the coating
material droplets.
[0082] In the alternative, other types of particle fluidized bed
spray coating can be employed. For example, the particles can be
suspended as a fluidized bed, and coated by spray application of a
coating material from above the fluidized bed. In another
alternative, the particles can be suspended in a fluidized bed, and
coated by spray application of a coating material from below the
fluidized bed, such as is described in detail above. In either
case, the coating material can be applied in either a batch process
or a continuous process. In coating devices used in continuous
processes, uncoated particles enter the fluidized bed and can
travel through several zones, such as a preheating zone, a spray
application zone, and a drying zone, before the coated particles
exit the device. Further, the particles can travel through multiple
zones in which different coating layers are applied as the
particles travel through the corresponding coating zones.
[0083] In the spinning disc method the granules and droplets of the
liquid coating material are simultaneously released from the edge
of a spinning disk, such as disclosed, for example, in U.S. Pat.
No. 4,675,140.
[0084] Other processes suitable for depositing uniform coating on
the granules will become apparent to those who are skilled in the
art.
[0085] For example, magnetically assisted impaction coating
("MAIC") available from Aveka Corp., Woodbury, Minn., can be used
to coat granules with solid particles such as titanium dioxide.
Other techniques for coating dry particles with dry materials can
also be adapted for use in the present process, such as the use of
a Mechanofusion device, available from Hosokawa Micron Corp.,
Osaka, JP; a Theta Composer device, available from Tokuj Corp.,
Hiratsuka, JP, and a Hybridizer device, available from Nara
Machinery, Tokyo, JP.
[0086] Depending on the nature of the binder used to prepare the
coating material, after application of the coating material to the
base particles to form a coating layer, it may be necessary to cure
the binder, as by application of heat, by application of
ultraviolet radiation, or the like. If the binder is dispersed in a
solvent such as water or an organic solvent, it may be necessary to
drive off the solvent from the coating material after application
of the coating material to the base particles to form a coating
layer in order to encourage film formation, or otherwise "cure" the
coating material. If the binder is a high solids material, cure may
be effected by simply permitting the coated particles to cool after
application of the coating material to the base particles to form a
coating layer at an elevated temperature.
[0087] As described above, in certain embodiments of the
disclosure, the base particle is a synthetic particle. As described
in more detail below, the present inventors have determined that
base particles having a desired geometry can be made by a variety
of methods from, for example, clays and other preceramic materials.
Examples of such materials include those described, for example, in
U.S. Pat. No. 7,811,730, U.S. Patent Applications Publications nos.
20100151199 and 20100203336, and U.S. Provisional Patent
Application No. 62/610,991, each of which is hereby incorporated
herein by reference in its entirety. For example, the base
particles can be formed by forming a preceramic material in desired
shapes, then firing that formed material to provide base particles.
The preceramic material can be, for example, a mixture of
particulate material with a suitable binder, such as the binders
otherwise described herein. A wide variety of particulate materials
can be used, e.g., stone dust, granule fines, can be used. In other
embodiments, a clay such as bauxite or kaolin can be used as the
preceramic material. Extrusion, casting or like process can in some
embodiments be used to provide base particles having the sizes and
aspect ratios. Examples of processes for providing base particles
having a predetermined desired shape are given by U.S. Pat. No.
7,811,630 incorporated herein by reference.
[0088] Additional methods for providing base particles of a desired
shape are described in more detail below.
[0089] In other embodiments, the solar-reflective roofing granules
of the collection are substantially formed from a single
composition. [That is, instead of coating a base particle with a
solar-reflective coating, substantially the entire granule can be
formed from solar-reflective material. Such granules can include
thin coatings on their outsides, e.g., formed of an organic or
silicone-based coating, but can otherwise be formed from a single
composition. Even though the materials are formed from a single
composition, there can be some differences in distribution of
materials or other properties within a single granule, e.g., with
certain components or properties being more evident at a surface as
compared to the bulk of the granule material.
[0090] The present inventors have determined that aluminosilicate
clay-containing compositions can be especially useful for making
particles and coatings as described herein. For example, in many
embodiments, the preceramic composition from which a particle or
coating is formed herein generally includes an aluminosilicate
clay, in certain embodiments, in combination with one or more
additives selected from a zinc source, a feldspar, nepheline
syenite and sodium silicate. Firing (i.e., heating of a material to
an elevated temperature) of the mixtures described herein can cause
both calcination and densification to result in a fired material
that is different in density and/or composition from the preceramic
mixture. In typical embodiments, some degree of both calcination
and densification (e.g., through sintering) occurs during the
firing process.
[0091] Notably, in certain embodiments of the granules as otherwise
described herein, the mineral outer surface of the mineral roofing
granules has a surface porosity of no more than about 10% as
measured by mercury porosimetry. For example, in certain
embodiments of the mineral roofing granules as otherwise described
herein, the mineral outer surface of the mineral roofing granules
has a surface porosity of no more than about 5% as measured by
mercury porosimetry. In other embodiments of the mineral outer
surface of the mineral roofing granules has a surface porosity of
no more than about 3% as measured by mercury porosimetry. In other
embodiments of the mineral outer surface of the mineral roofing
granules has a surface porosity of no more than about 2% as
measured by mercury porosimetry. In other embodiments of the
mineral outer surface of the mineral roofing granules has a surface
porosity of no more than about 1% as measured by mercury
porosimetry. As described above, the present inventors have
determined that a low surface porosity can provide for increased
resistance to long-term staining, e.g., a reduced "drop" in solar
reflectivity when applied to a heated bituminous roofing substrate.
The person of ordinary skill in the art will, based on the
description herein, select fireable mixtures, granulation methods
and firing conditions that provide a desirably low porosity. Such
low porosities can be provided, for example, when the
aluminosilicate-clay containing materials described here are used
as a coating or as the granule body.
[0092] In certain embodiments of the roofing granules as otherwise
described herein, the fired material is a fired mixture comprising
an aluminosilicate clay. As used herein, a "fired mixture" is
defined by the components of the mixture that is fired to form a
"fired material." The fired mixture is defined on dry basis, i.e.,
exclusive of any water or solvent that is used to provide the fired
mixture with formability. Aluminosilicate clays can be used to make
highly solar-reflective mineral roofing granules.
[0093] In certain embodiments of the mineral roofing granules as
otherwise described herein, the fired mixture further includes a
feldspar, nepheline syenite, and/or a sodium silicate. Materials
such as feldspars, nepheline syenite and sodium silicates can
increase the flowability of a clay material by lowering of the
melting point of the material and thus promoting liquefaction at a
given firing temperature, and as such can allow for a decreased
porosity.
[0094] In certain embodiments of the mineral roofing granules as
otherwise described herein, the fired mixture further includes a
zinc source. As the person of ordinary skill in the art will
appreciate, the zinc source can be converted in the firing to zinc
compounds such as zinc oxide, zinc silicates, zinc aluminosilicates
and zinc aluminates. As described in further detail below, the use
of a zinc source can not only provide algae resistance to the
mineral roofing granule, but can also provide a decreased porosity
at the mineral outer surface of the mineral roofing granule,
especially when used in combination with a feldspar, a sodium
silicate and/or a nepheline syenite. Zinc oxide can also provide
white color and increased solar reflectivity, and as such can be
helpful in providing the solar reflectivities described herein.
[0095] In certain embodiments of the roofing granules as otherwise
described herein, the aluminosilicate clay of the fired mixture is
a kaolin clay. As the person of ordinary skill in the art will
appreciate, a "kaolin clay" or "kaolin" is a material comprising
kaolinite, quartz and feldspar. For use in the mineral roofing
granules as described herein, it is desirable that the kaolin have
a kaolinite content of at least about 80 weight percent, for
example, at least about 90 weight percent, or even at least about
95 weight percent. As used herein, the amount of any feldspar,
nepheline syenite and sodium silicate present in the kaolin (or
other aluminosilicate clay) of a mixture to be fired is calculated
as part of the kaolin (or other aluminosilicate clay) component,
and not part of the feldspar, nepheline syenite or sodium silicate
component.
[0096] The person of ordinary skill in the art will appreciate that
a variety of types or grades of kaolin can be used. The kaolin used
in the mineral roofing granules described herein can be (or can
include), for example, a kaolin crude material, including kaolin
particles, oversize material, and ferruginous and/or titaniferous
and/or other impurities, having particles ranging in size from
submicron to greater than 20 micrometers in size. Alternatively, in
certain desirable embodiments, a refined grade of kaolin clay can
be employed, such as, for example, a grade of kaolin clay including
mechanically delaminated kaolin particles. Further, grades of
kaolin such as those coarse grades used to extend and fill paper
pulp and those refined grades used to coat paper can be employed in
the mineral roofing granules as described herein. Examples of
kaolins suitable for use in the mineral roofing granules as
described herein include, for example, EPK Kaolin (Edgar
Materials), for example in jet-milled form; Kaobrite 90 (Thiele
Kaolin); and SA-1 Kaolin (Active Minerals). Kaolins can be
subjected to any of a number of conventional processes to
beneficiate them, e.g., blunging, degritting, classifying,
magnetically separating, flocculating, filtrating, redispersing,
spray drying, pulverizing and firing.
[0097] In certain embodiments of the roofing granules as otherwise
described herein, a different aluminosilicate clay can be used in
combination with or instead of the kaolin. For example, in certain
embodiments of the roofing granules as otherwise described herein,
the aluminosilicate clay is (or includes) bauxite. In certain
embodiments of the roofing granules as otherwise described herein,
the aluminosilicate clay is (or includes) chamotte. In certain
embodiments of the roofing granules as otherwise described herein,
the aluminosilicate clay is (or includes) a white clay such as ball
clay or montmorillonite. In certain embodiments of the roofing
granules as otherwise described herein, the aluminosilicate clay is
(or includes) a white clay such as ball clay or montmorillonite.
However, in certain desirable embodiments, at least 50 wt %, e.g.,
at least 70 wt %, at least 80 wt %, at least 90 wt %, or even at
least 95 wt % of the aluminosilicate clay is kaolin.
[0098] The person of ordinary skill in the art will, on the basis
of the description provided herein, select aluminosilicate clay(s)
that provide a high degree of whiteness, and thus a high degree of
solar reflectivity. Two important impurities aluminosilicate clays
such as kaolin are iron and titanium. Iron can create
highly-colored impurities, especially upon firing and especially
when present in combination with titanium. Accordingly, in certain
desirable embodiments of the mineral roofing granules as otherwise
described herein, the aluminosilicate clay of the fired mixture has
no more than 1 wt % iron, e.g. no more than 0.7 wt % or no more
than 0.5 wt % iron, as measured by inductively-coupled plasma mass
spectrometry (ICP-MS) and reported as Fe.sub.2O.sub.3. Similarly,
in certain desirable embodiments of the mineral roofing granules as
otherwise described herein, the aluminosilicate clay of the fired
mixture has no more than 1 wt % titanium, e.g., no more than 0.7 wt
% no more than 0.5 wt % titanium, measured by ICP-MS and reported
as TiO.sub.2. The person of ordinary skill in the art can select
suitable clays having low amounts of iron and titanium.
[0099] In certain embodiments of the mineral roofing granules as
otherwise described herein, the aluminosilicate clay is present in
the fired mixture in an amount in the range of 40-90 wt % (i.e.,
exclusive of water or any solvent used to moisten the mixture for
formability). For example, in various embodiments of the mineral
roofing granules as otherwise described herein, the aluminosilicate
clay is present in the fired mixture in an amount in the range of
40-80 wt %, or 40-70 wt %, or 40-60 wt %, or 50-90 wt %, or 50-80
wt %, or 50-70 wt %, or 60-90 wt %, or 60-80 wt %, or 70-90 wt %.
The person of ordinary skill in the art will, based on the
disclosure herein, select an amount of aluminosilicate clay, e.g.,
in combination with other components, that provides the desired
solar reflectivity and stain resistance to the mineral roofing
granules.
[0100] In certain embodiments of the mineral roofing granules as
otherwise described herein, the fired mixture includes a feldspar.
As noted above, the feldspar of the fired mixture is a component
separate from any kaolin or other aluminosilicate clay present, and
thus the feldspar component is not said to include any feldspar
present in the kaolin or other aluminosilicate clay. As noted
above, the use of feldspar can lower the effective sintering
temperature of the overall fired mixture, and as such can provide
for a lower degree of surface porosity at a given firing
temperature. As the person of ordinary skill in the art will
appreciate, feldspars are aluminosilicates of sodium, potassium,
calcium and/or barium. Most commonly, the feldspars are considered
as solid solutions of three limiting compounds, soda feldspar,
potash feldspar and lime feldspar. Accordingly, in certain
embodiments of the mineral roofing granules as otherwise described
herein, the feldspar is one or more of a soda feldspar, a potash
feldspar, and a lime feldspar. For example, in certain embodiments
of the mineral roofing granules as otherwise described herein, the
feldspar is (or includes) a soda feldspar. In certain embodiments
of the mineral roofing granules as otherwise described herein, the
feldspar is (or includes) a potash feldspar. In certain embodiments
of the mineral roofing granules as otherwise described herein, the
feldspar is (or includes) a lime feldspar. MINSPAR.TM. 4 (Imerys)
is an example of a suitable feldspar for use in the mineral roofing
granules described herein. The person of ordinary skill in the art
will appreciate that other feldspars, such as plagioclase (solid
solution between albite and anorthite), alkali feldspars (solid
solutions between K-feldspar and albite) and barium feldspars can
be suitable for use in the preparation of the mineral granules as
otherwise described herein.
[0101] The person of ordinary skill in the art will, based on the
disclosure herein, select an amount of a feldspar, in combination
with the other component(s), that provides the desired solar
reflectivity and stain resistance to the mineral roofing granules.
For example, in certain embodiments of the mineral roofing granules
as otherwise described herein, the feldspar is present in the fired
mixture in an amount in the range of 2-40 wt % (i.e., exclusive of
water or any solvent used to moisten the mixture for formability).
In various embodiments of the mineral roofing granules as otherwise
described herein, the feldspar is present in the fired mixture in
an amount in the range of 2-30 wt %, or 2-25 wt %, or 2-20 wt %, or
2-15 wt %, or 2-15 wt %, or 5-40 wt %, or 5-30 wt %, or 5-25 wt %,
or 5-20 wt %, or 5-15 wt %, or 10-40 wt %, or 10-30 wt %, or 10-25
wt %, or 10-20 wt %, or 15-40 wt %, or 15-30 wt %, or 15-25 wt %,
or 20-40 wt %, or 20-35 wt %, or 20-30 wt %.
[0102] However, in other embodiments of the mineral roofing
granules as otherwise described herein, the fired mixture does not
include a substantial amount of feldspar (i.e., separate from any
feldspar in nepheline syenite that is present). For example, in
certain embodiments, the fired mixture includes less than 1 wt %,
less than 0.5 wt %, or even less than 0.2 wt % feldspar.
[0103] In certain embodiments of the mineral roofing granules as
otherwise described herein, the fired mixture includes a sodium
silicate (e.g., in combination with, or instead of the feldspar).
Like the feldspar, the sodium silicate of the fired mixture is a
component separate from any kaolin or other aluminosilicate clay
present, and thus the sodium silicate component is not said to
include any sodium silicate present in the kaolin or other
aluminosilicate clay. As noted above, the use of sodium silicate
can lower the effective sintering temperature of the overall fired
mixture, and as such can provide for a lower degree of surface
porosity at a given firing temperature.
[0104] The person of ordinary skill in the art will, based on the
disclosure herein, select an amount of a sodium silicate, in
combination with the other component(s), that provides the desired
solar reflectivity, stain resistance and low crystalline silica
content to the mineral roofing granules. For example, in certain
embodiments of the mineral roofing granules as otherwise described
herein, the sodium silicate is present in the fired mixture in an
amount in the range of 5-40 wt % (i.e., exclusive of water or any
solvent used to moisten the mixture for formability). In various
embodiments of the mineral roofing granules as otherwise described
herein, the sodium silicate is present in the fired mixture in an
amount in the range of 5-30 wt %, or 5-25 wt %, or 5-20 wt %, or
5-15 wt %, or 10-40 wt %, or 10-30 wt %, or 10-25 wt %, or 10-20 wt
%, or 15-40 wt %, or 15-30 wt %, or 15-25 wt %, or 20-40 wt %, or
20-35 wt %, or 20-30 wt %. Of course, in other embodiments,
substantially no separate sodium silicate component (i.e., separate
from the feldspar and/or nepheline syenite) is present in the fired
mixture. For example, in certain embodiments, the fired mixture
includes less than 1 wt %, less than 0.5 wt %, or even less than
0.2 wt % sodium silicate.
[0105] The person of ordinary skill in the art will, based on the
disclosure herein, select an amount of a nepheline syenite, in
combination with the other component(s), that provides the desired
solar reflectivity and low crystalline content to the mineral
roofing granules. For example, in certain embodiments of the
mineral roofing granules as otherwise described herein, the
nepheline syenite is present in the fired mixture in an amount in
the range of 2-40 wt % (i.e., exclusive of water or any solvent
used to moisten the mixture for formability). In various
embodiments of the mineral roofing granules as otherwise described
herein, the nepheline syenite is present in the fired mixture in an
amount in the range of 2-30 wt %, or 2-25 wt %, or 2-20 wt %, or
2-15 wt %, or 2-15 wt %, or 5-40 wt %, or 5-30 wt %, or 5-25 wt %,
or 5-20 wt %, or 5-15 wt %, or 10-40 wt %, or 10-30 wt %, or 10-25
wt %, or 10-20 wt %, or 15-40 wt %, or 15-30 wt %, or 15-25 wt %,
or 20-40 wt %, or 20-35 wt %, or 20-30 wt %. In certain
embodiments, when the fired mixture includes the nepheline syenite,
it does not include a substantial amount of feldspar. And in
certain embodiments, when the fired mixture includes the nepheline
syenite, it does not include a substantial amount of sodium
silicate.
[0106] However, in other embodiments of the mineral roofing
granules as otherwise described herein, the fired mixture does not
include a substantial amount of nepheline syenite. For example, in
certain embodiments, the fired mixture includes less than 1 wt %,
less than 0.5 wt %, or even less than 0.2 wt % nepheline
syenite.
[0107] In certain embodiments of the mineral roofing granules as
otherwise described herein, the fired mixture includes a zinc
source. As the person of ordinary skill in the art will appreciate,
the zinc source can be substantially any zinc compound that, when
fired together with an aluminosilicate source provides inorganic
zinc, e.g., in the form of one or more of a zinc oxide, a zinc
silicate, a zinc aluminosilicate and a zinc aluminate. For example,
in certain embodiments of the mineral roofing granules as otherwise
described herein, the zinc source is (or includes) zinc oxide. In
certain embodiments of the mineral roofing granules as otherwise
described herein, the zinc source is (or includes) one or more of
zinc oxide, zinc sulfide, zinc sulfate, zinc borate, a zinc
silicate, a zinc aluminate, or a zinc aluminosilicate.
Advantageously, the inventors have surprisingly found that the use
of a zinc source can surprisingly provide a lower porosity to a
fired material at a given firing temperature, especially when used
in combination with a feldspar, a nepheline syenite and/or a sodium
silicate. The use of a zinc source can also provide a mineral
roofing granule with algae resistance, and can also provide
increased whiteness to the fired material overall.
[0108] The person of ordinary skill in the art will, based on the
disclosure herein, select an amount of a zinc source, in
combination with the other component(s), that provides the desired
solar reflectivity and stain resistance to the mineral roofing
granules. For example, in certain embodiments of the mineral
roofing granules as otherwise described herein, the zinc source is
present in the fired mixture in an amount in the range of 1-30 wt %
(i.e., exclusive of water or any solvent used to moisten the
mixture for formability). In various embodiments of the mineral
roofing granules as otherwise described herein, the sodium silicate
is present in the fired mixture in an amount in the range of 1-25
wt %, or 1-20 wt %, or 1-15 wt %, or 5-30 wt %, or 5-25 wt %, or
5-20 wt %, or 15-30 wt %, or 10-25 wt %, or 15-30 wt %. The zinc
source can be provided in a variety of particle sizes. In certain
embodiments, the particle size (median) of the zinc source (e.g.,
ZnO) can be in the range of 50-500 nm, e.g., 100-500 nm, 50-250 nm,
or 100-200 nm.
[0109] The zinc source can in some cases be transformed during
firing to one or more different zinc compounds. The person of
ordinary skill in the art will appreciate that the zinc makeup of
the fired material will depend on, e.g., the particular composition
of the zinc source used, the firing conditions (e.g., time and
temperature), and the particular composition(s) of the other
component(s) of the fired mixture. In certain embodiments of the
mineral roofing granules as otherwise described herein, at least
50% (e.g., at least 60%, at least 70%) of the zinc present in the
fired material is present as a zinc oxide or a zinc silicate, as
determined by X-ray crystallography. In other embodiments of the
mineral roofing granules as otherwise described herein, at least
50% (e.g., at least 60%, at least 70%) of the zinc present in the
fired material is present as a zinc oxide, a zinc aluminate, a zinc
aluminosilicate or a zinc silicate, as determined by X-ray
crystallography. And in certain desirable embodiments of the
roofing granules as otherwise described herein, no more than 40%
(e.g., no more than 30%, no more than 20%) of the zinc present in
the fired material is present as ZnAl.sub.2O.sub.4, as determined
by X-ray crystallography. ZnAl.sub.2O.sub.4 is much less leachable
at acidic pH than other commonly-used forms of zinc (e.g., ZnO and
Zn silicate). Through selection of components in the mixtures to be
fired and of firing temperatures based on the disclosure herein,
the person of ordinary skill in the art can provide a desired
balance of ZnAl.sub.2O.sub.4 as compared to other zinc forms, and
thereby provide a desired overall rate of leaching. As demonstrated
by Y. Tang et al., Environmental Technology, 36: 23, 2977-2986
(2015), ZnAl.sub.2O.sub.4 tends to form at higher firing
temperatures. Use of a feldspar, a nepheline syenite, or a sodium
silicate together with a zinc source can be unexpectedly advantaged
in that it can allow for firing at lower temperatures to provide a
given level of porosity and solar reflectivity, and allow the
person of ordinary skill in the art to provide material with a
desirable relative amounts of ZnAl.sub.2O.sub.4 with respect to
other zinc forms in an as-fired material. The person of ordinary
skill in the art will, based on the description herein, select
amounts of feldspar, nepheline syenite and/or sodium silicate,
amounts of zinc source and firing conditions to provide the desired
algae resistance in combination with a desired solar reflectivity,
a desired level of crystalline silica, and a desired stain
resistance.
[0110] In certain embodiments of the mineral roofing granules as
otherwise described herein, the fired material is a fired
aluminosilicate material including in the range of 1-30 wt % zinc,
measured on a zinc oxide basis (i.e., assuming that all zinc is in
the form of ZnO). In certain such embodiments, the zinc is present
in the fired material in an amount in the range of 1-25 wt %, or
1-20 wt %, or 1-15 wt %, or 5-30 wt %, or 5-25 wt %, or 5-20 wt %,
or 10-30 wt %, or 10-25 wt %, or 10-30 wt %. The person of ordinary
skill in the art will appreciate that the fired material can
include a number of different crystalline phases. However, in
certain desirable embodiments, the fired material includes less
than 10 wt %, less than 5 wt %, less than 2 wt %, or even less than
1 wt % cristobalite. The inventors have noted that the use of
feldspar, nepheline syenite and/or sodium silicate as described
herein can allow for relatively low firing temperatures, below the
temperature at which significant amounts of crystalline silica
phases (especially cristobalite and quartz) can form. And,
critically, the inventors have determined that even at high firing
temperatures, mixtures including nepheline syenite can provide very
low amounts of crystalline silica. This can allow for relatively
high firing temperatures to be used to provide a low surface
porosity, without creating an undesirably high amount of
crystalline silica.
[0111] The fired material has been described above with respect to
its position at the mineral outer surface of a roofing granule. The
fired material can be present, for example, through at least a
depth of 50 microns of the mineral roofing granule. In certain
embodiments, the fired material is present through at least a depth
of 100 microns, or even 200 microns of the mineral roofing
granule.
[0112] In certain embodiments of the mineral roofing granules as
otherwise described herein, the composition of the mineral body of
the mineral roofing granule is substantially homogeneous
throughout. That is, the mineral body, extending substantially to
the mineral outer surface, has a substantially homogeneous
composition. This does not, however, mean that there is no phase or
material separation within the mineral body. Rather, "substantially
homogeneous" is used here to signify that there is no large-scale
region (e.g., having a diameter of 200 microns) of the mineral body
that is different in overall composition from another large-scale
region (e.g., having a diameter of 200 microns) of the mineral
body.
[0113] In certain embodiments of the mineral roofing granules as
otherwise described herein, the porosity of the mineral body is
substantially homogeneous throughout. That is, the mineral body,
extending substantially to the mineral outer surface, has a
substantially homogeneous porosity.
[0114] However, in other embodiments of the mineral roofing
granules as otherwise described herein, the porosity of the mineral
body is substantially higher than the porosity at the mineral outer
surface. For example, without intending to be bound by theory, the
inventors surmise that in some cases the feldspar, nepheline
syenite and/or sodium silicate can migrate to the particle surface,
providing a higher degree of densification and therefore a lower
porosity than in the rest of the mineral roofing granule even in a
mineral roofing granule made from a single fired mixture. And in
some embodiments, multiple fired mixtures can be used to make the
mineral roofing granules, with a higher amount of one or more of
the zinc source, feldspar, nepheline syenite and/or sodium silicate
in the mixture used at the mineral outer surface of the mineral
roofing granule. This, too, can lead to increased densification and
therefore lower porosity at the surface. A higher degree of
porosity in the mineral body can help to improve solar reflectivity
of the mineral roofing granule.
[0115] Granules and base particles made from the preceramic
mixtures described herein can be made by forming a green granule or
particle (e.g., as generally described above, and described in more
detail below), then firing the green granule or particle to provide
the granule or particle. The firing converts the mixture to the
fired composition.
[0116] The first mixture can have the mineral components as
described above (e.g., as identified and in the same amounts) with
respect to the first fired mixture. Moreover, as the person of
ordinary skill in the art will appreciate, the first mixture can
further include one or more solvents (e.g., water, an organic
solvent such as a lower alcohol). As noted above, the amount of the
solvent is not used in the calculation of the amounts of the
components of a such a mixture to be fired. The first mixture can
also further include an organic binder. As the person of ordinary
skill in the art will appreciate, a binder can improve pelletizing
and other forming processes, and can help to increase the strength
of the green granules. Suitable binders include, for example, a
starch, a resin, a wax, a glue such as AR animal glue, gelatinized
cornstarch, calcium carbonate and polyvinyl alcohol. Such a binder
can be used in amounts, for example, up to 6 wt % of the first
mixture, e.g., up to 3% or up to 2%.
[0117] Again, the aluminosilicate clay-containing materials
described here can be used not only as a material for a roofing
granule, but also in the alternative as a coating for a base
particle (e.g., made of slate). Such uses are described in U.S.
Provisional Patent Application No. 62/610,991, which is hereby
incorporated herein by reference in its entirety.
[0118] FIG. 2 is a cross-sectional schematic view of a coated
solar-reflective roofing granule of the disclosure. Granule 200 has
a base particle 210, coated by solar-reflective coating 220.
[0119] FIG. 3 is a cross-sectional schematic view of another
solar-reflective roofing granule of the disclosure. Granule 300 is
formed substantially from a single composition, e.g., from an
aluminosilicate clay-containing fireable mixture. The granule
presents a solar reflective surface due to the granule being
substantially formed from a solar reflective material. Such
granules can, of course, have thin coatings formed thereon, as long
as such a coating does not make the overall granule non-reflective.
For example, such a coating can be derived from a material selected
from silanes, siloxanes, polysiloxanes, organo-siloxanes,
silicates, organic silicates, silicone resins, acrylics, urethanes,
polyurethanes, glycol ethers and mixtures thereof. Examples of
coatings and methods for coating are described in U.S. Pat. App.
Publication no. 20110081537, U.S. Pat. Nos. 7,241,500, 3,479,201,
3,255,031, and 3,208,571, all of which are incorporated herein by
reference in their entirety for all purposes. In certain desirable
embodiments, the coating has a transmittance to visible radiation
of at least 80%, at least 90%, or even at least 95%. In the
embodiment of FIG. 3, granule 300 includes a thin coating 315 at
its outer surface.
[0120] Another aspect of the disclosure is a roofing product
comprising a substrate; a bituminous material coated on the
substrate, the bituminous material having a top surface; and a
collection of solar-reflective roofing granules as described herein
disposed on the top surface of the bituminous material, thereby
substantially coating the bituminous material. The roofing products
of the disclosure can be configured, e.g., in the form of a roofing
shingle, or in the form of a roofing membrane.
[0121] One embodiment of such a roofing product is shown in
schematic cross-sectional view in FIG. 4. In the embodiment of FIG.
4, roofing product 430 includes substrate 440, having a bituminous
material 450 disposed thereon. Bituminous material 450 has top
surface 452. As the person of ordinary skill in the art will
appreciate, the bituminous material can be coated on both surfaces
of, or even saturate the roofing substrate. A variety of materials
can be used as the substrate, for example, conventional bituminous
shingle or membrane substrates such as roofing felt or fiberglass.
A collection of solar-reflective roofing granules 400 is disposed
on the top surface 452 of the bituminous material 450, such that
they substantially coat the bituminous material in a region 455
thereof. The region can be, for example, the exposure zone of a
shingle, or a region that is otherwise to be exposed when the
roofing product is installed on a roof. The solar-reflective
roofing granules are desirably embedded somewhat in the bituminous
material to provide for a high degree of adhesion. As the person of
ordinary skill in the art will appreciate, other granular or
particulate material can coat the bituminous material in regions
that will not be exposed, e.g., on a bottom surface of the roofing
product, or in a headlap zone of a top surface of the roofing
product, as is conventional.
[0122] Notably, the present inventors have determined that the
orientation of the solar-reflective roofing granules can have an
important impact on the solar reflectivity of the overall roofing
product. In certain desirable embodiments as otherwise described
herein, the roofing product has a major plane, wherein each roofing
granule has a major axis, a minor axis perpendicular to the major
axis, and a thickness, and wherein for at least 90% (counted
numerically) of the roofing granules having a major aspect ratio of
at least 4, the major axis and the minor axis are disposed within
20 degrees of parallel to the major plane of the roofing product.
The present inventors have noted that the overall roughness of the
surface of the roofing product has a significant effect on the
solar reflectivity, and that orienting the granules to be close to
parallel to the surface can help to provide a low apparent
roughness. In certain such embodiments, for at least 90% of the
roofing granules having a major aspect ratio of at least 4the major
axis and the minor axis are disposed within 10 degrees of parallel
to the major plane of roofing product.
[0123] Moreover, even if most of the granules are oriented
substantially parallel to the major plane of the roofing products,
if there are significant numbers of the granules that are not
oriented substantially parallel to the surface, they can
undesirably increase surface roughness. Accordingly, in certain
embodiments as otherwise described herein, no more than 30% of
granules (e.g., no more than 20% or even no more than 10%) having a
major aspect ratio of at least 4 are disposed with their major axis
or minor axis disposed more than 40 degrees from parallel to the
major plane of the roofing product. In certain such embodiments, no
more than 30% of granules (e.g., no more than 20% or even no more
than 10%) having a major aspect ratio of at least 4 are disposed
with their major axis or minor axis disposed more than 30 degrees
from parallel to the major plane of the roofing product. In certain
such embodiments, no more than 30% of granules (e.g., no more than
20% or even no more than 10%) having a major aspect ratio of at
least 4 are disposed with their major axis or minor axis disposed
more than 20 degrees from parallel to the major plane of the
roofing product. And in certain embodiments, no more than 10%
(e.g., no more than 5%) of the granules having a major aspect ratio
of at least 4 are disposed with their major axis or minor axis
disposed more than 70 degrees from parallel to the major plane of
the roofing product. In certain embodiments, no more than 10%
(e.g., no more than 5%) of the granules having a major aspect ratio
of at least 4 are disposed with their major axis or minor axis
disposed more than 60 degrees from parallel to the major plane of
the roofing product. In certain embodiments, no more than 10%
(e.g., no more than 5%) of the granules having a major aspect ratio
of at least 4 are disposed with their major axis or minor axis
disposed more than 50 degrees from parallel to the major plane of
the roofing product.
[0124] As noted above, the solar-reflective roofing granules of the
collection substantially coat the top surface of the bituminous
material in a region thereof. In certain embodiments, the roofing
product has a bituminous area fraction of no more than 10% in the
region substantially coated by the solar-reflective roofing
granules of the collection. For example, in certain embodiments,
the roofing product has a bituminous area fraction of no more than
5%, no more than 3%, or no more than 2%, on the solar-reflective
roofing granule-coated top surface of the bituminous material. The
bituminous area fraction is the area fraction in which bituminous
material is visible, e.g., between the areas occluded by the
granules. Bituminous area fraction can be determined via
conventional image processing methods.
[0125] The present inventors have determined that using granules of
relatively large size as described elsewhere herein can provide for
a reduction in solar reflectivity by providing a relatively low
boundary concentration. As used herein, a boundary concentration is
the number of interfaces between granules per unit area. A roofing
membrane covered with small particles will have more granule
interfaces per unit area than a roofing membrane covered with large
particles at the same % bituminous area fraction. Boundary
concentration is measured by the procedure described in the example
below. For example, in certain embodiments, the boundary
concentration is no more than 3.0%, e.g., no more than 2.5% or even
no more than 2.0%.
[0126] Notably, the present inventors have determined that the
surface roughness of the overall roofing product has a significant
effect on solar reflectivity of the product. In certain desirable
embodiments, a roofing product as otherwise described herein has a
surface roughness (Sq) of no more than 350 .mu.m, e.g., no more
than 300 .mu.m or even no more than 250 .mu.m, as measured by
optical profilometry (e.g., laser triangulation, interferometry, or
chromatic confocal profilometry).
[0127] Use of the roofing granules as described herein, e.g.,
oriented as described herein, can provide solar-reflective roofing
products with high solar reflectivity. In certain embodiments as
otherwise described herein, a roofing product has a solar
reflectivity of no less than 60%, e.g., no less than 62% or no less
than 64%. Solar reflectivity of a roofing product is determined
using a solar reflectometer pursuant to ASTM C1549.
[0128] A variety of methods can be used to fabricate the roofing
products described herein. For example, conventional
granule-dropping methods can be used, especially when the
bituminous surface is sufficiently soft that a pressing operation
can tilt the granules into the desirable orientation.
[0129] The present inventors have noted, however, even when soft a
bituminous material can be very sticky, meaning that a pressing
operation may not be effective in in some cases in providing the
most desired orientations of granules. Thus, the present inventors
note that the provision of roofing products with flat granules with
both high coverage and an orientation substantially parallel to the
roofing product surface can be difficult, and have invented a
convenient method for providing such a roofing product.
Accordingly, another aspect of the disclosure is a method for
making a roofing product as described herein. The method includes
providing a substrate having a bituminous material disposed
thereon, the bituminous material having a top surface, the top
surface of the bituminous material being in a softened state. Also
provided is a collection of solar-reflective roofing granules as
described herein. The solar-reflective roofing granules of the
collection are oriented in a substantially single layer on a
substantially upward-facing first, non-adhesive surface having a
major plane such that for at least 90% of the roofing granules the
major axis and the minor axis are disposed within 20 degrees of
parallel (e.g., within 10 degrees of parallel) to the major plane
of the first non-adhesive surface. Then, the solar-reflective
roofing granules of the collection so oriented are transferred to
the top surface of the softened bituminous material without
substantially changing their orientation.
[0130] One such embodiment is shown in schematic view in FIG. 5. In
the embodiment of FIG. 5, solar reflective roofing granules 500 are
oriented in a substantially single layer on first non-adhesive
surface 560, which is facing substantially upward. For example, the
first non-adhesive surface can be oriented within 20 degrees of
parallel to the ground, e.g., 10 degrees of parallel to the ground.
The granules are oriented such that for at least 90% of the roofing
granules the major axis and the minor axis are disposed within 20
degrees of parallel to the major plane of the first non-adhesive
surface. In certain embodiments, the orienting includes disposing
the solar-reflective roofing granules of the collection on the
first, non-adhesive surface, and then vibrating (e.g., shaking) the
first non-adhesive surface under conditions to cause the
solar-reflective roofing granules of the collection to orient in a
substantially single layer on the first, non-adhesive surface such
that for at least 90% of the roofing granules the major axis and
the minor axis are disposed within 20 degrees of parallel to the
major plane of the first non-adhesive surface. The person of
ordinary skill in the art can determine vibrating conditions to
provide the desired orientation for a given collection of
particles; for example, various types of shaking motions can cause
the granules to orient in a desired fashion through the influence
of gravity. The granules are then transferred to the top surface of
a softened bituminous material disposed on a substrate without
substantially changing their orientation (i.e., at the time of the
transfer). In the embodiment of FIG. 5, the transfer includes
contacting the top surface 552 of a softened bituminous material
550 in a substantially downward-facing orientation against the
layer of roofing granules 500 on the first non-adhesive surface,
thereby adhering the granules to the top surface of the softened
bituminous material. As the person of ordinary skill in the art
will appreciate, this can be performed in a variety of ways, e.g.,
using conveyer belts and continuous processing as is common in the
art.
[0131] Another method is shown in cross-sectional schematic view in
FIG. 6. The method includes bringing a second, tacky surface 680 in
a substantially downward-facing orientation against the layer of
roofing granules 600 on the first non-adhesive surface 660, thereby
adhering the oriented granules to the tacky surface, contacting the
top surface 652 of the softened bituminous material 650 with the
layer of roofing granules on the second tacky surface, thereby
transferring the granules from the second tacky surface to the top
surface of the softened bituminous material.
[0132] The present inventors have noted above that it can be
desirable to include a proportion of smaller granules on the
surface of a roofing product, so that they can fill gaps between
larger roofing granules. These smaller granules can have a high
aspect ratio as described above. But in other embodiments, the
smaller granules need not have a high aspect ratio. Thus, a roofing
product can be provided as otherwise described herein, with two
types of granules disposed on its top surface: the granules of a
collection of granules as otherwise described herein; and a second
set of granules having a particle size smaller than #30 mesh. The
second set of granules can fill in gaps between the larger granules
of the collection. The granules of the collection of granules as
otherwise described herein desirably forms at least 70 wt % (e.g.,
at least 80 wt %) of the total granular material on the
granule-coated top surface of one or more zones (e.g., one or more
exposure zones) of the roofing product. The second set of granules
is desirably solar reflective as described above for the
collections of roofing granules, although they need not have the
high aspect ratio as described above. A two-step method can be used
to make such roofing products. First, the granules of a collection
as described herein can be disposed on the bituminous material
(e.g., using a method as described above), then the granules of the
second set can be applied to fill in any gaps between the granules
of the collection.
[0133] Another aspect of the disclosure is a method for making a
collection of solar-reflective roofing granules as described
herein. The method includes providing a formable fireable
preceramic material forming the preceramic material into a
collection of wet preceramic particles having a high aspect ratio;
and drying and firing the collection of wet preceramic particles to
provide a collection of granular particles having a high aspect
ratio. As described in more detail below, these particles can be
further coated to provide roofing granules as described herein, or
in other embodiments can themselves be suitable for use as roofing
granules as described herein.
[0134] The person of ordinary skill in the art will appreciate that
a variety of formable fireable preceramic materials can be used to
form the granular particles described herein. The materials
described above with respect to synthetic granules and synthetic
granule cores can be used, for example. And the person of ordinary
skill in the art will appreciate that a variety of other preceramic
materials, e.g., based on clays or other ceramic systems, can be
used. The formable material can be, for example, moistened with
water or some other suitable liquid to provide formability. A
polymeric binder can also or alternatively be used as is common in
the ceramic arts; such a binder can soften under pressure to bind
the particles, then be burned away during firing. Of course, for
some compositions, no liquid or organic binder is necessary to
provide formability under pressure.
[0135] The formable fireable preceramic material can be formed into
a collection of wet preceramic particles having a high aspect
ratio. A variety of forming techniques can be used. For example,
the preceramic material can be extruded into a thin ribbon or
sheet, then cut or broken into shapes with a desired aspect ratio.
For example, a cutter disposed at the output of an extruder can be
used to cut the ribbon or sheet of preceramic material into the
desired shapes.
[0136] In one especially desirable embodiment, the forming of the
material is performed by roll compaction. Roll compaction can be
used to form a thin sheet of material, which can then be cut or
broken into particles of the desired shape. In other embodiments,
at least one roll of the roll compactor has a mold surface formed
thereon. The mold surface of the roll compactor can be configured
to form desired high aspect ratio shapes from the material. In
certain embodiments, the mold surface is configured to form
granules all having substantially similar shapes. Such granules can
be suitable, for example, for commercial roofing applications, in
which aesthetic considerations are less important. However, in
other embodiments, the mold surface is configured to form granules
having a variety of different shapes. The mold surface can provide,
e.g., at least four, at least ten, or even at least twenty
different shapes. With a larger number of different shapes, the
granules can be more suitable for use in residential roofing
applications, where a more random appearance is desired. The person
of ordinary skill in the art can select roll compaction parameters
to provide a collection of preceramic particles that are robust
enough to be fired.
[0137] FIG. 7 is a schematic view of a method for using roll
compaction to form granular particles
[0138] Here, a formable material is passed between two rollers,
spaced closely apart at a nip. The left-hand roller has a mold
surface formed thereon, configured to form the formable material
into granular particles. As the rollers roll, the formable material
is flattened between them and cut into granular pieces by the mold
surface of the roller.
[0139] The method further includes firing the preceramic particles
of the collection to provide a collection of granular particles
having a high aspect ratio. The person of ordinary skill will
select firing conditions (e.g., with any desirable drying steps) to
provide robust granular particles.
[0140] The dimensions of the particles can be provided to provide a
desired shape and size to the granules of the final collection of
roofing granules (e.g., after any coating or other operations). The
aspect ratios and sizes described above with respect to the roofing
granules can likewise be selected from the granular particles made
by the methods described herein.
[0141] The granular particles themselves can be used as a base
particle to make the coated granules described above. Thus, in
certain embodiments, the method further includes coating the high
aspect ratio particles of the collection with a coating, such as a
solar-reflective coating as described above. The coating can be
performed on the fired particles, or alternatively can be performed
on the preceramic particles with a preceramic coating, with the
firing serving to fire both the material of the particles and the
material of the coating.
[0142] In other embodiments, the granular particles can themselves
be the solar-reflective roofing granules. Of course, as described
above, other thin coatings can be formed thereon (e.g., silane or
siloxane coatings).
[0143] The following non-limiting examples serve to further explain
the roofing granules, roofing products and methods of the
disclosure.
Granule Size
[0144] A set of granule packing experiments was designed to
determine the effect of granule size on coverage and appearance. A
sieve separation was conducted to separate a sample of commercial
white granules into the fractions shown in Table 1, below
TABLE-US-00001 TABLE 1 US Sieve Range Wt % of total +12 8% 12\16
43% 16/20 27% 20/30 18% 30/40 4% -40 negligible
[0145] Shinglets were made from each fraction and two granule
blends as shown in Table 2, below, using conventional granule
application methods on small asphalt-coated substrates. The color
(L*, a* and b*), Solar Reflectivity (SR), and coverage (% black)
were measured and are also listed in Table 2. L*, a*, b* and SR are
the average of three measurements. % black is calculated from the
measured asphalt exposed over 12 measurements across the shinglet
surface (the old % coverage method).
TABLE-US-00002 TABLE 2 Sample Sieve % black no. size L* a* b* SR
Average stdev 1 +12 81.12 -0.17 2.87 0.572 14.8 1.5 2 12\16 81.92
-0.06 3.34 0.587 15.0 1.5 3 16/20 79.81 0.09 3.91 0.557 17.9 2.1 4
20/30 84.74 -0.36 2.67 0.615 12.6 0.4 5 30/40 80.16 -0.12 3.49
0.542 16.7 1.1 6 50/50 12/16 + 80.89 0.04 3.83 0.565 15.7 1.6 16/20
7 50/50 12/16 + 76.7 0.32 4.49 0.520 25.1 3.4 30/40
[0146] The data presented in Table 2 appear to demonstrate an
effect of particle size on SR and color. Surprisingly, the 20/30
sample delivered a higher SR and a lighter color.
[0147] The SR measurements presented in Table 2 were obtained
within two days of making the shinglets. At this point, all of the
granules appeared white. After one month of aging in laboratory
conditions under room lighting at room temperature, however, the
granules became stained. The staining is shown in the photographs
of FIG. 8, for samples 1-5 (in which the left-most sample is the
most white, with increasing color moving right). This is a known
problem for white granules placed on top of modified asphalt, as
low molecular weight compounds from the asphalt diffuse into the
oil on the granules. One surprising result, however, was how much
more severe the staining was for smaller granules when compared to
larger ones.
[0148] Additional shingle samples were made from blends of 20/30
granules and 30/40 granules, as well as from 20/30 granules and
30/40 granules alone. Data for these samples is shown in Table 3,
below:
TABLE-US-00003 TABLE 3 Granule Shingle % % Median % % S.sub.a 20/30
30/40 (.mu.m) Span asphalt boundaries (.mu.m) SR 0 1 608 0.50 17.1
4.29 229 0.516 0.2 0.8 641 0.61 16.8 4.18 230 0.521 0.5 0.5 709
0.65 13.9 3.84 235 0.551 0.8 0.2 786 0.58 16.0 3.72 273 0.552 1 0
826 0.49 17.0 3.43 327 0.561
[0149] The data indicate that SR decreases as particle size
decreases (a higher percentage of 30/40 granules are added to the
blend). There was no change in coating thickness or exposed asphalt
to explain this behavior. Furthermore, the surface roughness
decreases with decreasing particle size, a trend that in isolation
should increase the SR. Therefore, it is concluded for this data
set the SR is dominated by the boundary concentration. A higher
number of small particles in the granule distribution results in a
higher number of boundary locations in which light can become
trapped.
[0150] Boundary concentration was determined by quantifying the
magnitudes in the grayscale gradient variations of images taken of
the samples. Essentially, the idea was based on the fact that in
areas where there is light-trapping, i.e. granule boundaries, there
is a perceived localized discontinuation that is translated into a
variation in the grayscale value in each color plane. Hence, if the
most significant gradient variations could be isolated, it was
envisaged that this would give an indication as to the level
significance of granule boundaries that are present. It was
hypothesized these grain boundaries played a significant role in
light trapping. A typical example can be seen in FIG. 9, which is a
set of images showing grayscale value intensity variations, and the
accompanying gradient magnitude map for 30/40 granules (left
images) and 16/20 granules (right images). The top set of images is
a false-color rendering of the grayscale values. The second set of
images show the rate of change of the localized grayscale values,
following the application of a Sobel edge amplification
algorithm.
[0151] What can be observed in the bottom set of images in FIG. 9
is the level of light interaction in the boundaries. Extensive
morphological operations were performed to obtain a set of boundary
skins shown in FIG. 10, along with a second set of superimposed
images shown in the second row. It can be seen from FIG. 10 that
the granule boundaries are substantially identified. It is clear
from FIG. 10 that the sample made from smaller granules (left side)
has more boundaries per unit area than the sample made from large
granules (right side). The area fraction of boundaries identified
by this method is used for comparison across the various
samples.
[0152] Shingle solar reflectivities were measured for a variety of
shingles made from sorted commercial white granules. FIG. 11
correlates SR with measured shingle roughness (Sa) as measured by
optical profilometry and median granule particle size (Q50). The
data demonstrate that for a given surface roughness, shingles with
smaller particle sizes have lower SR values.
Granule Shape
[0153] In addition to the granule size, we also expect the granule
shape to affect the appearance and SR of the shingles. A vibratory
shape sorter (FIG. 12, full view; FIG. 13, view of sorting table
with white roofing granules separating over the table) was used to
separate the granules by shape. While traveling over the vibrating
table, the rounder granules are more likely to roll and segregate
to the lower numbered bins (left side of the table). The more
angular granules are more likely to slide and tumble and segregate
to the higher numbered bins (right side of the table).
[0154] The distribution of granules (by weight) in each bin at the
end of sorting is shown in FIG. 14. The table conditions (table
angles, vibration amplitude, and feed rate) can be adjusted to
change this distribution to be flatter or closer to normal. Visual
inspection indicated that that the granules in bin 1 are rounder in
shape while those in bin 12 are flakey (see the pictures of FIG.
15). The granules in the intermediate bins have intermediate
shapes.
[0155] The solar reflectivity of the granules were evaluated in a
petri dish using a portable reflectometer. There were not enough
granules in some bins to sufficiently fill the dish (for example
bins 2-4), so these bins were combined. The solar reflectivity of
the granules was found to vary across the table as shown in FIG.
16. The center of each diamond represents the mean, with lines
above and below the centerline representing the 95% confidence
interval. The data in FIG. 12 can be divided into three
reflectivity groupings. The lowest reflectivities come from bins
5-8, medium reflectivity from bins 1-4 and bin 9, and higher
reflectivities from bins 10-12. The differences in reflectivity are
likely a result of packing in the petri dish. For this measurement,
the granules are poured into a glass petri dish, and the bottom of
a second glass petri dish is used to tap the top surface flat. When
bins 10-12 were subject to this tapping, the flaky granules laid
down to produce a relatively flat surface with minimal light
trapping. The rounder granules (bins 1-4) were not able to produce
a relatively flat surface upon tapping.
[0156] Granules from certain bins were pressed onto black plastic
tapes to approximate shingles. The solar reflectivities (SR) of
these test samples were measured and are shown in FIG. 17. The
solar reflectivity was found to be equivalent for tape shingles
made from the different granules. This was a surprising result, in
light of the differences in granule SR shown in FIG. 17. However,
the granule orientation was not controlled on these tape samples.
Even though the granules are pressed into the shingle, they are
constrained by the sticky tape (mimicking the asphalt in many
conventional shingle coating methods) and are not able to rotate as
they are when packed into the petri dish. This was attempted both
using the black tape as well as pressing the granules directly into
asphalt patties. In both cases, a difference in SR was not observed
between granules from different bins.
Granule Orientation
[0157] Typically, test shingles are made by placing an asphalt
patty or black tape face up and pouring the granules onto the tape.
A roller is then used to press the granules into the tape. This
approximates conventional granule coating processes used in
manufacturing of roofing products. The orientation is not
controlled during the standard process, so the granule orientation
is considered to be substantially random.
[0158] A different set of tape samples were made with granules
oriented parallel to the tape surface or "flattened", using the
method shown in FIG. 18.
[0159] The SR was measured for tape samples made with random and
flattened granule orientations and the results are shown in FIG.
19. The SR is higher for all samples with flat orientation. The
inventors surmise that a higher measured SR results when the
surface roughness is lower and so the probability that a reflected
ray will hit another granule is smaller. For the flakey granules
(20/30 bin 12) we find the increase in SR to be approximately 7
points, bringing the average SR from 60.5 to 67.4.
[0160] Additional aspects of the disclosure are provided by the
following enumerated embodiments, which can be combined and
permuted in any number and in any combination that is not
technically or logically inconsistent.
Embodiment 1
[0161] A collection of solar-reflective roofing granules having a
solar reflectivity of at least 70%, at least 70 wt % (e.g., at
least 80 wt % or at least 90 wt %) of the solar-reflective roofing
granules of the collection having a major aspect ratio of at least
4 and a minor aspect ratio of at least 3.
Embodiment 2
[0162] The collection of solar-reflective roofing granules
according to claim 1, wherein at least 70 wt % (e.g., at least 80
wt % or at least 90 wt %) of the solar-reflective roofing granules
of the collection have a major aspect ratio of at least 6, e.g., at
least 8.
Embodiment 3
[0163] The collection of solar-reflective roofing granules
according to claim 2, wherein at least 70 wt % (e.g., at least 80
wt % or at least 90 wt %) of the solar-reflective roofing granules
of the collection have a minor aspect ratio of at least 5, e.g., at
least 7.
Embodiment 4
[0164] The collection of solar-reflective roofing granules
according to any of claims 1-3, wherein in at least 70 wt % (e.g.,
at least 80 wt % or at least 90 wt %) of the solar-reflective
roofing granules of the collection the ratio of the major axis to
the minor axis is in the range of 1-2.
Embodiment 5
[0165] The collection of solar-reflective roofing granules
according to any of claims 1-3, wherein in at least 70 wt % (e.g.,
at least 80 wt % or at least 90 wt %) of the solar-reflective
roofing granules of the collection the ratio of the major axis to
the minor axis is 1-1.5, or in the range of 1-1.33.
Embodiment 6
[0166] The collection of solar-reflective roofing granules
according to any of claims 1-5, wherein at least 90 wt % of the
solar-reflective roofing granules of the collection have a particle
size in the range of 1/4'' US mesh to #50 US mesh, e.g., #5 US mesh
to #50 US mesh.
Embodiment 7
[0167] The collection of solar-reflective roofing granules
according to any of claims 1-6, wherein at least 50 wt % (e.g., at
least 70 wt %, at least 80 wt % or at least 90 wt %) of the
solar-reflective roofing granules have a particle size in the range
of 1/4'' US mesh to #30 US mesh, for example, 1/4'' US mesh to #25
US mesh, #5 US mesh to 30 US mesh, or #5 US mesh to #25 US
mesh.
Embodiment 8
[0168] The collection of solar-reflective roofing granules
according to any of claims 1-6, wherein at least 50 wt % (e.g., at
least 70 wt %, at least 80 wt % or even at least 90 wt %) of the
solar-reflective roofing granules have a particle size in the range
of 1/4'' US mesh to #20 US mesh, for example, #5 US mesh to 20 US
mesh, 1/4'' US mesh to 15 US mesh, #5 US mesh to #15 US mesh or #10
US mesh to #20 US mesh.
Embodiment 9
[0169] The collection of solar-reflective roofing granules
according to any of claims 1-6, wherein at least 50 wt % (e.g., at
least 70 wt %, at least 80 wt % or even at least 90 wt %) of the
solar-reflective roofing granules have a particle size in the range
of #12 US mesh to #20 US mesh, for example, #16 US mesh to #20 US
mesh.
Embodiment 10
[0170] The collection of solar-reflective roofing granules
according to any of claims 1-9, wherein at least 10% by weight
(e.g., at least 15 wt %, at least 20 wt %, or even at least 30 wt
%) of the granules of the collection have a particle size in excess
of #20 mesh (e.g., in excess of #30 mesh).
Embodiment 11
[0171] The collection of solar-reflective roofing granules
according to any of claims 1-10, having a solar reflectivity of at
least 75%, at least 80%, or even at least 85%.
Embodiment 12
[0172] The collection of solar-reflective roofing granules
according to any of claims 1-11, wherein the solar-reflective
roofing granules of the collection substantially comprise a base
particle having a solar-reflective coating disposed thereon.
Embodiment 13
[0173] The collection of solar-reflective roofing granules
according to claim 12, wherein the base particle is crushed slate,
slate granules, shale granules, mica granules, metal flakes.
Embodiment 14
[0174] The collection of solar-reflective roofing granules
according to claim 12, wherein the base particle is a synthetic
particle.
Embodiment 15
[0175] The collection of solar-reflective roofing granules
according to any of claims 12-14, wherein the coating comprises a
coating binder and a solar reflective pigment.
Embodiment 16
[0176] The collection of solar-reflective roofing granules
according to claim 15, wherein the coating binder is selected from
the group consisting of metal silicates, fluoropolymers, metal
phosphates, silica coating binders, sol-gel coating binders,
polysiloxanes, silicones, polyurethanes, and polyacrylates.
Embodiment 17
[0177] The collection of solar-reflective roofing granules
according to claim 15 or claim 16, wherein the solar-reflective
pigment is selected from the group consisting of titanium dioxide,
calcium carbonate, zinc oxide, lithopone, zinc sulphide, white
lead, glass microspheres, glass microbubbles, microvoid pigments,
and synthetic polymeric opacifiers
Embodiment 18
[0178] The collection of solar-reflective roofing granules
according to any of claims 12-14, wherein the solar-reflective
coating comprises an aluminosilicate clay.
Embodiment 19
[0179] The collection of solar-reflective roofing granules
according to any of claims 1-11, wherein the solar-reflective
roofing granules of the collection substantially are formed from a
single composition.
Embodiment 20
[0180] The collection of solar-reflective roofing granules
according to any of claims 1-19, the collection of solar-reflective
roofing granules is white in color, and has
(a*.sup.2+b*.sup.2).sup.1/2 less than 6.
Embodiment 21
[0181] A roofing product comprising [0182] a substrate; [0183] a
bituminous material coated on the substrate, the bituminous
material having a top surface; and [0184] the collection of
solar-reflective roofing granules according to any of claims 1-20
disposed on the top surface of the bituminous material, thereby
substantially coating the bituminous material in a region
thereof.
Embodiment 22
[0185] The roofing product according to claim 21, in the form of a
roofing shingle.
Embodiment 23
[0186] The roofing product according to claim 21, in the form of a
roofing membrane.
Embodiment 24
[0187] The roofing product according to any of claims 21-23, the
roofing product having a major plane, wherein each roofing granule
has a major axis, a minor axis perpendicular to the major axis, and
a thickness, and wherein for at least 90% of the roofing granules
having a major aspect ratio of at least 4 the major axis and the
minor axis are disposed within 20 degrees of parallel to the major
plane of the roofing product.
Embodiment 25
[0188] The roofing product according to any of claims 21-23, the
roofing product having a major plane, wherein each roofing granule
has a major axis, a minor axis perpendicular to the major axis, and
a thickness, and wherein for at least 90% of the roofing granules
having a major aspect ratio of at least 4 the major axis and the
minor axis are disposed within 10 degrees of parallel to the major
plane of the roofing product.
Embodiment 26
[0189] The roofing product according to any of claims 21-25,
wherein no more than 30% of granules (e.g., no more than 20% or
even no more than 10%) having a major aspect ratio of at least 4
are disposed with their major axis or minor axis disposed more than
40 degrees (e.g., no more than 30 degrees or even no more than 20
degrees) from parallel to the major plane of the roofing
product.
Embodiment 27
[0190] The roofing product according to any of claims 21-26,
wherein no more than 10% (e.g., no more than 5%) of the granules
having a major aspect ratio of at least 4 are disposed with their
major axis or minor axis disposed more than 70 degrees (e.g., more
than 60 degrees or more than 50 degrees) from parallel to the major
plane of the roofing product.
Embodiment 28
[0191] The roofing product according to any of claims 21-27,
wherein the roofing product has a bituminous area fraction of no
more than 10% in the region substantially coated by the
solar-reflective roofing granules of the collection.
Embodiment 29
[0192] The roofing product according to any of claims 21-28,
wherein the roofing product has a bituminous area fraction of no
more than 5%, no more than 3%, or no more than 2% in the region
substantially coated by the solar-reflective roofing granules of
the collection.
Embodiment 30
[0193] The roofing product according to any of claims 21-29, having
a boundary concentration of no more than 3.0%, e.g., no more than
2.5% or even no more than 2.0%.
Embodiment 31
[0194] The roofing product according to any of claims 21-30, having
a surface roughness (Sq) of no more than 350 .mu.m, e.g., no more
than 300 .mu.m or even no more than 250 .mu.m.
Embodiment 32
[0195] The roofing product according to any of claims 21-31, having
a solar reflectivity of no less than 60%, e.g., at least 62% or at
least 64%.
Embodiment 33
[0196] A method for making a roofing product according to any of
claims 21-32, comprising [0197] providing a substrate having a
bituminous material disposed thereon, the bituminous material
having a top surface, the top surface of the bituminous material
being in a softened state; and [0198] providing a collection of
solar-reflective roofing granules according to any of claims 1-20;
[0199] orienting the solar-reflective roofing granules of the
collection in a substantially single layer on a substantially
upward-facing first, non-adhesive surface having a major plane such
that for at least 90% of the roofing granules the major axis and
the minor axis are disposed within 20 degrees of parallel to the
major plane of the first non-adhesive surface; and then [0200]
transferring the solar-reflective roofing granules of the
collection to the top surface of the softened bituminous material
without substantially changing the orientation of the
solar-reflective roofing granules of the collection.
Embodiment 34
[0201] The method according to claim 33, wherein the orienting
includes disposing the solar-reflective roofing granules of the
collection on the first, non-adhesive surface, and then vibrating
the first non-adhesive surface under conditions to cause the
solar-reflective roofing granules of the collection to orient in a
substantially single layer on the first, non-adhesive surface such
that for at least 90% of the roofing granules the major axis and
the minor axis are disposed within 20 degrees of parallel to the
major plane of the first non-adhesive surface.
Embodiment 35
[0202] The method according to claim 33 or claim 34, wherein the
transferring includes contacting the top surface of the softened
bituminous material in a substantially downward-facing orientation
against the layer of roofing granules on the first non-adhesive
surface, thereby adhering the granules to the top surface of the
softened bituminous material.
Embodiment 36
[0203] The method according to claim 33 or claim 34, wherein the
transferring includes bringing a second, tacky surface in a
substantially downward-facing orientation against the layer of
roofing granules on the first non-adhesive surface, thereby
adhering the granules to the tacky surface, contacting the top
surface of the softened bituminous material with the layer of
roofing granules on the second tacky surface, thereby transferring
the granules from the second tacky surface to the top surface of
the softened bituminous material.
Embodiment 37
[0204] A method for making a collection of solar-reflective roofing
granules according to any of claims 1-20, the method comprising
[0205] providing a formable fireable preceramic material; [0206]
forming the preceramic material into a collection of preceramic
particles having a high aspect ratio; and [0207] firing the
collection of preceramic particles to provide a collection of
granular particles having a high aspect ratio.
Embodiment 38
[0208] The method according to claim 37, wherein the forming is
performed by roll compaction.
Embodiment 39
[0209] The method according to claim 38, wherein the roll compactor
includes a mold surface formed on one or more rolls thereof, the
mold surface being configured to form high aspect ratio shapes from
the material.
Embodiment 40
[0210] The method according to claim 39, wherein the mold surface
provides at least four different shapes.
Embodiment 41
[0211] The method according to claim 37, wherein the forming is
performed by extrusion.
Embodiment 42
[0212] The method according to any of claims 37-41 further
comprising coating the high aspect ratio particles of the
collection with a coating, e.g., a solar-reflective coating.
Embodiment 43
[0213] The method according to any of claims 37-41, further
comprising coating the collection of wet preceramic particles with
a preceramic coating before firing the collection.
Embodiment 44
[0214] The method according to any of claims 37-41, wherein the
solar-reflective roofing granules of the collection substantially
are formed from a single composition.
[0215] It will be apparent to those skilled in the art that various
modifications and variations can be made to the processes and
devices described here without departing from the scope of the
disclosure. Thus, it is intended that the present disclosure cover
such modifications and variations of this invention provided they
come within the scope of the appended claims and their
equivalents.
* * * * *